A Frequency Domain Approach for Fatigue Life Estimation from Finite Element Analysis

Fatigue damage is traditionally determined from time signals of loading, usually in the form of stress or strain. This approach is satisfactory for periodic loading but requires very large time records to accurately describe random loading processes. These may prove prohibitive for many finite element analyses especially when modelling dynamic resonance. Alternatively, a compact frequency domain fatigue calculation can be utilised where the random loading and response are categorised using Power spectral density (PSD) functions and the dynamic structure is modelled as a linear transfer function. This paper will review the available methods for performing fatigue analysis from PSDs and shows that the Dirlik method gives the best comparable results with the traditional time domain approaches. It also demonstrates how these techniques can be implemented in the Finite Element environment to rapidly identify critical areas in the structure.